When I study magnetic properties this is most complicated concept for me. How to determine the relationship of particle size and magnetic property. What happens when we decrease particle size? What is the effect of particle size in Ms (magnetization) and Hc ?
State of magnetic saturation is the state when all magnetic moments in a sample are in parallel to external field. So, Ms is arithmetical sum of all magnetic moments in the sample divided by sample volume. When the sample consists of (nano)particles (grains) in general, Ms is not dependent on size of particles. I see 2 reasons which can change Ms, if we decrease particle sizes: 1. atoms near particle surface can have other electronic configuration than internal atoms ; 2. density of the sample material (its volume) can be changed.
Simply speaking, Hc characterizes of magnetization reversal of material. The process of reversal is going by 2 main mechanisms: domain walls moving and magnetic rotation of domain magnetic moment. Hc is parameter which strongly dependent on material microstructure and so: on particle shapes and sizes. It comes from that facts:
1. a definite size of magnetic domains exist as a result of competition of exchange interaction energy and magnetic interaction energy. When particle sizes decrease, the particles can consists of 1 domain only and so we will not need to provide external energy (by applying external field) for moving of domain walls.
2. easy magnetization axis and crystallographic anisotropy exist in material. Crystallographic anisotropy also can decrease with particle size: so we will need less external field for rotation of magnetic moment of particle.
Of course, other types of anisotropy can be important (shape anisotropy, as example).
As for the magnetization it is quite simple. Near the surface of the particle the magnetization is different from the magnetization in the volume. The volume fraction of the surface layer varies with the size of the particle (L) as 1/ L. The average magnetization of the particle varies according to the same law.
thanks for your answers friend I need more clarification about it so only I ask in here
Magnetic nanoparticles (single-domain) show a widerange of unusual magnetic properties as compared to the respective bulk materials (multi-domains) which strongly influenced by finite-size, surface effects, environment such as interparticle and particle–matrix interactions. Surface effects can be related to the symmetry breaking of the crystal structure at the boundary of each particle can also be due to different chemical and magnetic structures of internal “core” and surface “shell” parts of a nanosized particle. In particles with size below some characteristic value, the coercivity decreases with decreasing particle size if the temperature is higher than blocking temperature. Surface effects are due to the lack of translational symmetry at outer boundaries of a particle, reduced coordination number, and broken magnetic exchange bonds of surface atoms. Decreasing the particle size gradually increases the ratio of surface spins to the total number of spins.The surface influence is most significant in smallest nanoparticles and vanish for very large particles. Physical properties of the surface and the core of a nanoparticle can differ very much. Finite-size and surface effects can dramatically change the magnetic properties of nanoparticle in comparison with corresponding ‘‘bulk’’ counterpart. It should bear in mind that since the magnetic parameters (the saturation magnetization and the crystalline anisotropy) are sensitive to temperature and external magnetic field, then critical radii can also be temperature and field dependent. The surface effects can be also shape-dependent since the relative number of surface atoms depends on the particle shape. The surface effects can also lead to so-called "exchange bias".
I not sure what you are asking but, I am guessing that on a monochromatic frequency scale when a micro-organism is stimulated it can be identified by the color that it illuminates. This is according to the Rife experiments. So I am thinking if this is so, could a particulate have the same out come, and could a pleomorphic reaction take place and would we be able to follow each state as it changed just by stimulating its bio sphere? Hmmmmmmmmm????
nano particles depend upon their physical structure: the size and the shape of the particles, their micro structure, and the chemical phases.
when size of the particle low ,then Saturation Magnetization Ms is the maximum value of magnetic induction and Remanence magnetization (Mr or Br) means when the applied field approaches zero, magnetic material still retains some of its induction called remanence magnetization, Because of the overall resistance provided by the area walls on the direction of the applied field. Soft loop means low energy losses and high electrical resistivity).
Dear Gregory Leitus
I want to thank you for your interesting response, and ask you if you could introduce a source to learn about the magnetic behaviour of nanoparticles and their mechanisms. I would appreciate it very much.
When the particle size is small ,leades to increase the magnetic properties and coresev force it's very high can you reading about hysteric magnetic loop in the matels
Dear Rusul A. Rsool . This is for example the case of coercivity vs. particle diameter.
Dear Dr. Yassine Sliman
Yes when small size particle ,that manens material is superpara magentic ..and a high magantic properties .can be shown in your schemi.
Dear Dr. Rusul A. Rsool ,
I am sorry to say NO.
For the case of SPM, the coercive field is equal to zero practically (no coercivity).
For the saturation magnetizion, Largely, it decreases (not increases) with decreasing the particle size.
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